1. Field of the Invention
The present invention relates to a process for removing peroxides from peroxide containing aqueous waste streams such as those from the propylene oxide/styrene monomer technology so that the treated stream can be further processed prior to its disposal.
2. Description of the Prior Art
The Oxirane process for the production of propylene oxide and styrene monomer is a process of very great commercial importance. The basic patent describing this process is U.S. Pat. No. 3,351,635. In a version of the process, ethylbenzene is oxidized to ethylbenzene hydroperoxide, the ethylbenzene hydroperoxide is catalytically reacted with propylene to form propylene oxide and 1-phenyl ethanol, and the 1-phenyl ethanol is dehydrated to form styrene monomer.
In practice of the process there are a number of separation and recovery steps and various purge streams are formed which must be disposed of in the face of ever increasing environmental concerns. In various instances, disposal practices which were permitted in the past may, in the future, no longer be permitted. Accordingly, considerable efforts are being directed to bring about improvements in procedures used to treat propylene oxide/styrene monomer purge streams.
One such purge stream is an acidic wastewater removed as a distillation sidestream. In the Oxirane propylene oxide and styrene monomer process, ethylbenzene is reacted with molecular oxygen to produce ethylbenzene hydroperoxide. See, for example, U.S. Pat. No. 4,066,706. Vapor from the oxidation is contacted with cool ethylbenzene in order to absorb contained ethylbenzene from the vapors and to effect economies of heat recovery. Normally a liquid acidic aqueous sidestream is recovered from the contact/absorption zone of the absorber and an overhead vapor stream mainly comprised of nitrogen is also recovered. The acidic wastewater contains in addition to water and various organic acids, significant amounts of peroxidic materials. Consideration has been given to biotreatment of such streams but the contained organics tend to flash in a biopond exceeding VOC limits. First stripping organics before biotreatment is an option but this would result in dangerous concentrations of peroxides forming within the stripper.
In U.S. Pat. No. 5,993,673, a procedure for decomposing peroxidic materials is shown wherein the acidic aqueous stream is contacted with a solid iron promoted alumina catalyst to effect such decomposition. It is disclosed that a nitrogen sweep gas is employed to remove oxygen which is formed by the peroxide decomposition.
In such systems, the provision of a independent source of nitrogen represents a significant process expense. In accordance with the present invention, however, nitrogen vapor from the oxidizer is used to sweep the oxygen which results from peroxide decomposition thus avoiding the need and expense of separately purchased nitrogen.
In accordance with the invention, acidic aqueous process streams containing organic acids, peroxidic materials and ethylbenzene are contacted with a catalyst at conditions effective to decompose the peroxidic materials and the oxygen formed by the decomposition is swept using at least a portion of the nitrogen vapor effluent from the ethylbenzene oxidation whereby the formation of explosive gas mixtures is avoided.